Cell Membrane and Fluid Mosaic Model Notes

Learning Objectives

  • Understand the cell membrane fluid mosaic model
  • Describe functions of phospholipids, proteins, and carbohydrates in membranes
  • Discuss membrane fluidity

Plasma Membrane Functions

  • Defines cell boundaries, mediates interactions with the environment
  • Regulates substance exchange (exclusion, intake, excretion)
  • Flexible for shape changes in cells (e.g., red and white blood cells)
  • Contains markers for cell recognition (crucial for tissue formation and immune response)
  • Integral proteins transmit signals and act as receptors for hormones and growth factors, with potential for viral hijacking (e.g., HIV)

Fluid Mosaic Model

  • Proposed by Davson and Danielli in 1935, refined by Singer and Nicolson in 1972
  • Describes plasma membrane as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates
  • Plasma membranes are 5 to 10 nm thick, with variability among cell types

Components of Plasma Membrane

1. Phospholipids
  • Composed of glycerol, two fatty acids, and a phosphate group
  • Form a lipid bilayer with hydrophilic heads facing outward and hydrophobic tails inward
2. Proteins
  • Integral proteins span the membrane and interact with phospholipids
  • Peripheral proteins are located on inner or outer surfaces and may function in signaling or structural roles
3. Carbohydrates
  • Located on the exterior surface, forming glycoproteins and glycolipids
  • Critical for cell recognition and interaction with the environment; form the glycocalyx (sugar coating)

Membrane Fluidity

  • Fluid mosaic structure allows for movement of molecules; integral proteins float within the bilayer
  • Fluidity affected by phospholipid saturation: saturated fats (rigid) vs. unsaturated fats (flexible)
  • Cholesterol maintains membrane fluidity across varying temperatures

Career Connection: Immunology

  • Immunologists study immune responses, vaccine development, and cellular recognition
  • Important for combating infectious diseases and understanding autoimmune disorders
  • Training includes advanced education (PhD or MD) and specialized programs
  • Example: Kizzmekia S. Corbett and her work on COVID-19 vaccine development